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Issue 36, 2018
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Cyclooctatetraenyl calcium and strontium amido complexes

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This paper reports the synthesis and structural characterisation of a series of cyclooctatetraenyl (C8H8) complexes of calcium and strontium, most of them containing the bis(trimethylsilyl)amido ligand. Mixing MI2 (M = Ca, Sr), KN(SiMe3)2 and K2(C8H8) in thf in a 2 : 2 : 1 ratio gave the inverse sandwich amido complexes [[{(Me3Si)2N}M(thf)x]2(μ-C8H8)] (M = Ca, x = 1; M = Sr, x = 2) (1-Ca, 1-Sr) in fair to good yields. From a 1 : 1 : 1 ratio, the mixed potassium calcium complex [[{(Me3Si)2N}Ca(thf)](μ-C8H8)K] (2) was obtained in good yield. The reaction of 2 with a 1 : 1 mixture of CaI2 and KN(SiMe3)2 yielded 1-Ca confirming that the reaction could be carried out stepwise. Attempts at making heterobimetallic calcium strontium amido complexes from the reaction of 2 with Sr{N(SiMe3)2}2 led to redistribution reactions which afforded the potassium strontium complex [[K{(Me3Si)2N}2Sr]2(μ-C8H8)] (3) among other species. Complex 3 was more conveniently synthesised in fair yield starting from a 2 : 4 : 1 molar mixture of SrI2, KN(SiMe3)2 and K2(C8H8), respectively. Treatment of 2 with PhC[triple bond, length as m-dash]CH in benzene yielded an insoluble complex tentatively formulated as the polymeric complex [CaK(CCPh)(C8H8)(thf)x]n (4). Upon dissolution in thf, 4 underwent a redistribution reaction yielding the X-ray characterised [{Ca(μ-C8H8)2}K2(thf)2] (5) and a homoleptic calcium alkynyl complex [Ca(CCPh)2(thf)x]. Several compounds were characterised by X-ray diffraction as discrete or polymeric structures where Ca⋯Cπ interactions were identified in some cases. Despite identified drawbacks, such as the lability of the coordinated thf ligands and facile redistribution reactions, this study represents the first synthetic approach to cyclooctatetraenyl heavy alkaline-earth metal amido complexes.

Graphical abstract: Cyclooctatetraenyl calcium and strontium amido complexes

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The article was received on 01 Jun 2018, accepted on 12 Jun 2018 and first published on 13 Jun 2018

Article type: Paper
DOI: 10.1039/C8DT02257G
Citation: Dalton Trans., 2018,47, 12587-12595
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    Cyclooctatetraenyl calcium and strontium amido complexes

    F. M. Sroor, L. Vendier and M. Etienne, Dalton Trans., 2018, 47, 12587
    DOI: 10.1039/C8DT02257G

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